his brother's in hospital and he doesn't seem at all worried o bothered o perturbed

me dijo que se lo había llevado ella y se quedó tan tranquila

she told me she had taken it, as cool as you like o as cool as a cucumber o quite unashamedlyshe told me, quite calmly o boldly, that she had taken it

el tren pasó casi rozando y ellos se quedaron tan tranquilos

the train passed within an inch of us and they didn't turn a hair o they didn't bat an eyelash (inglés norteamericano) o (inglés británico) eyelidthe train passed within an inch of us and they were quite unperturbed

lo dijo mal y se quedó tan tranquilo

he said it wrong but he just carried on regardless o as if nothing had happenedhe said it wrong but he was completely unfazed o unabashed